1. Field of The Invention
This invention relates in general to the field of applicators and in particular to an applicator having a high speed non-contact extrusion valve for use in automated assembly line operations.
2. Description of The Prior Art
Where a fluid is applied or supplied to various products, including but not limited to adhesive for paper cartons, paper towels, envelopes, labels, or other like products, it is typical that applicators be used to apply the fluid. In adhesive applications, the adhesive may be in the form of small dots, thin dashed or solid lines, large dots or broad dashed or solid lines. The lines or dots are usually applied in a direction coincident with the direction of travel of the product as it travels past the fixed position of the applicator.
As noted in the background section of U.S. Pat. No. 4,488,665 to Cocks, et al., adhesive applicators first utilized in the prior art were air actuated, whereby a built-in air cylinder was used to lift a shutoff needle from a seat to permit the dispensing of a pressurized adhesive. Air-operated actuators have been found to be inherent limitations in applying adhesives in high speed assembly line applications. For example, they are not sufficiently responsive for high-speed production, where their use results in misapplication of the amount of the adhesive and mislocation of the placement of the adhesive. If the adhesive is misplaced or applied at the wrong location, the product may be spoiled and perhaps be rejected as unsatisfactory. Similarly, if insufficient adhesive is applied, the glued joint may be weaker or stronger than required. Then, if an attempt is made to overcome an insufficiency of adhesive by applying additional adhesive at additional locations where such additional locations are not critical to the product, the cost of such additional adhesive may unnecessarily and materially add to the costs of production. Thus, for every application there is an optimum condition of applying the exact amount of adhesive at the desired location at the fastest possible production speed. For such adhesive applications, applicators are required which dispense the adhesive and respond accurately and repeatedly to input control signals.
Attempts have been made to overcome the inherent disadvantages in high speed air-operated applicators by the use of sophisticated electronic equipment to operate the solenoid valves for purposes of controlling the air used to operate the applicator; however, such attempts have not in general been totally satisfactory. In high speed applications, electronic control of the air still resulted in an excessive time delay between the operation of the valve and the subsequent operation of the air cylinder in the applicator. This time delay was not consistent and varied inasmuch as sealing packings within the valve changed characteristics with heat and use, causing inconsistencies in application of the adhesive when responding to the same signal.
The use of airless, solenoid-operated adhesive spray applicators have overcome some of the above-noted problems of the air-operated applicators. In such applicators, the adhesive is applied without the use of compressed air. Upon activation, a solenoid unseats a spring-loaded plunger which then permits a pressurized adhesive to flow through the valve and onto the product. One example of an airless, solenoid-operated valve of this type is disclosed in U.S. Pat. No. 3,212,715 to Cocks. In fact, the basics of the Cocks '715 patent are also utilized in the Cocks, et al. '665 patent relating to a multiple-outlet adhesive applicator.
Although airless, solenoid-operated applicators are known in the prior art, high speed assembly line operations generally have been limited by the performance characteristics thereof. In particular, the time required for the valve in an applicator to open and close, as well as the time required by the applicator before the valve can repeat this cycle, are functional requirements which manufacturers in the industry are continually attempting to improve upon. Principally, this is because the less time taken to open and close the valve (i.e., the faster the valve opens and closes), the greater the ability to perform shorter and more precise adhesive patterns, which translates into use of less glue during an operation (and less cost). Most importantly, however, shortening the time for opening and closing the valve, as well as reducing the time required before the applicator is ready to repeat the cycle, enables a conveyor carrying the product to be run at a faster speed and/or the product to be placed closer together on the conveyor, each of which increases production.
Accordingly, a primary object of the present invention is to provide an applicator having a non-contact extrusion valve which requires a minimum time for opening and closing.
Another object of the present invention is to provide an applicator which requires a minimum amount of time before recycling.
Still another object of the present invention is to provide an applicator having a coil which generates a maximum electromagnetic field and pole pieces which have maximum susceptibility to the electromagnetic field.
Yet another object of the present invention is to provide an applicator having a solenoid coil which minimizes the time required to generate and collapse an electromagnetic field.